Within the Colobinae, the genera Rhinopithecus (snub-nosed monkeys), Pygathrix (douc langurs) and Nasalis (proboscis monkeys and simakobus) are informally grouped as the odd-nosed monkeys. While these genera comprise an eclectic mix featuring remarkable natural histories, this ecologically diverse group previously received little attention from the scientific community. In the last decade, however, a plethora of new and exciting research has occurred on these understudied colobines. In this book, we present a summary and synthesis of this new knowledge, looking to compare across taxa and scientific disciplines and generate in-depth discussion of what odd-nosed monkeys can tell us about the unity and diversity of the primates as a whole. This review follows the central themes of primatology and covers topics as diverse as taxonomy and phylogeny, functional morphology, spatial and dietary ecology, activity patterns, social organisation, life histories and ends with an overview of the conservation status of these enthralling and endangered primates.